Other features of the present invention are discussed and claimed in commonly assigned and co-pending U.S. application Ser. No. 10/003,990, filed on Oct. 31, 2001 entitled xe2x80x9cAir Mass Flow Rate Determinationxe2x80x9d.
The present invention relates generally to engine control systems for internal combustion engines, and more particularly, to a method and apparatus for determining an air mass flow rate target used to provide torque control to internal combustion engines having a pressurized induction system.
In general, internal combustion engines have at least one inlet manifold for supplying air or a combustible mixture of air and fuel to the engine combustion spaces. To increase the charge of combustible mixture that is supplied to the combustion spaces of the engine, it is common to employ pressurized induction systems, such as blowers and turbochargers, which increase the amount of air delivered to the combustion spaces of the engine. Since fuel is metered to the engine as a function of the mass of air delivered to the combustion spaces, the amount of fuel delivered to the combustion spaces is also increased so as to maintain proper air/fuel ratio. As such, various performance aspects of the engine, such as power output and/or efficiency, can be improved over normally aspirated induction systems.
Turbochargers are a well known type of pressurized induction system. Turbochargers include a turbine, which is driven by exhaust gas from the engine, and a compressor, which is mechanically connected to and driven by the compressor. Rotation of the compressor typically compresses intake air which is thereafter delivered to the intake manifold. The pressure differential between the compressed air and the intake manifold air is known as turbo boost pressure.
At various times during the operation of the engine, it is highly desirable to increase, decrease or eliminate turbo boost pressure to control engine torque to suit the given operating condition. This is typically implemented by controlling the amount of exhaust gas provided to the turbocharger. One common method for controlling the amount of exhaust gas delivered to the turbocharger is a wastegate valve, which is employed to bypass a desired portion of the exhaust gas around the turbine. Most automotive turbochargers use a wastegate valve to control the amount of exhaust gas supplied to the turbine blades. By controlling the amount of exhaust gas that is bypassed around the turbine, the intake air flow is controlled, thereby controlling the turbo boost pressure, the pressure in the intake manifold, and the engine torque. Therefore, it is important to determine how much exhaust gas must be bypassed for a given operating condition. If too much exhaust gas is bypassed, not enough torque will be produced. Conversely, if not enough exhaust gas is bypassed, engine and/or driveline damage may occur due to excessive torque loading.
Methods for controlling the wastegate are well known in the industry. Conventional systems attempt to control the boost pressure by xe2x80x9cbleeding offxe2x80x9d gas as boost pressure becomes too high. However, these conventional pressure-based systems are reactionary and have several drawbacks. In particular, control systems now often employ model based fueling methods which are based on air flow characteristics. Because most other current fueling models target air flow to determine fuel delivery characteristics, it has also become desirable to target air flow to provide torque control for engines with pressurized induction systems (such as turbochargers, superchargers, etc.).
In order to determine such an air flow target, certain data, such as the amount of air flowing through the throttle body for any operating condition, must be acquired. A method and system for providing this data are described in commonly assigned co-pending U.S. patent application Ser. No. 10/003,990 entitled xe2x80x9cAir Mass Flow Rate Determinationxe2x80x9d, which is incorporated by reference as if fully set forth herein. Briefly, the method and system provide the determination of an air mass flow rate target for pressurized induction systems. The air mass flow rate target is indicative of the mass flow rate of compressed air exiting the compressor of the turbocharger assembly. The air mass flow rate target can be determined based on obtaining two components, namely, a reference air mass flow rate term and a compressibility term. The reference air mass flow rate term is obtained through a series of operations which include the determination of a throttle valve position and an air bypass valve position.
Specifically, a throttle position is determined from a signal sent from a throttle position sensor. A throttle position sonic air flow term is bench mapped in a look up table based on throttle position and sonic air flow.
The air bypass valve position is determined from its controlling current sent from an air bypass valve position sensor. An air bypass valve sonic airflow term is bench mapped in a look up table based on the air bypass position and sonic air flow.
The throttle sonic air flow term and the air bypass valve sonic air flow term are then summed to obtain a total throttle and air bypass sonic air flow term, herein referred to as the reference air mass flow rate term.
The compressibility term is determined through a series of operations, including the sensing of engine rotational speed via a sensor. Once the engine rotational speed is determined, the reference air mass flow rate term and the engine rotational speed are input into a surface look up table to obtain a predicted pressure ratio. The predicted pressure ratio is representative of the ratio of pressure at the intake manifold, or manifold absolute pressure (MAP), compared to the pressure before the throttle body, or throttle inlet pressure. A processor performs a mathematical manipulation to derive the compressibility term based in part on the predicted pressure ratio.
The compressibility term is input into a processor along with the reference air mass flow rate term 62. The processor then performs a mathematical manipulation to derive the air mass flow rate target.
It is desirable to utilize the air mass flow rate target data to determine an air flow target to thereby control engine torque for any operating condition and maintain the torque at certain levels in all operating conditions.
In one embodiment, the present invention provides a method for characterizing an air flow target within an internal combustion engine. The method includes determining an engine rotational speed, an air bypass valve position and a throttle position. The engine rotational speed, air bypass valve position and throttle valve position are processed to obtain an air mass flow rate target. The engine rotational speed and air mass flow rate target are then processed to determine the air flow target.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.